Communication in Distributed Systems

Tom Kelliher, CS43

Feb. 22, 1996

Communication Protocols

A set of rules followed by two processes (systems, people) which are communicating. The protocol governs how the communication is carried out.



The pathway of communication between two computers. It may be a single wire, or a set of wires connected via switches (routers, gateways, bridges, etc.). The circuit may be dedicated or virtual.

Connection-Oriented protocols (TCP)

Connectionless protocols (IP, UDP)

The OSI Model

(Open Systems Interconnection Reference Model)

Seven layered abstract model of a protocol stack:

Advantages: modularity

Disadvantages: call overhead; size increases due to added headers, trailers

Physical Layer



Data Link Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

``Library''-type functionality

Application Layer

User- System-Level utilities:

Introduction to TCP/IP

Some of the protocols:

Message transmission example:

``Gluing'' Networks Together

IP Addresses



  1. Data
  2. Application layer
  3. TCP/UDP layer --- TCP frame
  4. IP layer --- IP datagram
  5. Ethernet layer --- ethernet frame: 46--1500 bytes (MTU)


Process Communication

How do processes on separate machines communicate?

Thomas P. Kelliher
Wed Feb 21 17:07:49 EST 1996
Tom Kelliher